User vs Position

There are a number of groups that need to have participation by whomever occupies a 'position' in the organization, for example 'Office Manager'. 

We assign an individual to be the 'Office Manager'.

I would like to add the 'Office Manager' to multiple groups so that when there is a new person in that role, I don't have to ferret out and add the new person to the various groups. And I want each group to see that 'Office Manager' is a member -not the individual.

I would also like the individual to have their own user email account. I don't see how to accomplish that with an alias for the individual. And I don't want to consume a second license for the same person using the role of 'Office Manager'.

How do I create a user account for 'Office Manager', assign a user to the Office Manager account, so that when there is a change in the office manager occupant, all i have to do is assign the new individual the role of 'Office Manager' and all group membership immediacy apply?

It doesn't seem that it should be difficult?